The "O.P. Tree" was an Observation Post Tree deployed during World War I. Its "goal," as author Hanna Rose Shell explains in Hide and Seek, her newly published history of the relationship between camouflage and photography, "was to craft a mimetic representation of a tree-and not just any tree, but a particular tree at a specific site" on the European battlefield.

The design, fabrication, and, perhaps most interestingly, installation of this artificial plant form had a fascinating and somewhat Truman Show-esque quality:

To develop the O.P. Tree, Royal Engineers representatives selected, measured, and photographed the original tree, in situ, extensively. The ideal tree was dead; often it was bomb blasted. The photographs and sketches were brought back to the workshop, where artists constructed an artificial tree of hollow steel cylinders, but containing an internal scaffolding for reinforcement, to allow a sniper or observer to ascend within the structure. Then, under the cover of night, the team cut down the authentic tree and dug a hole in the place of its roots, in which they placed the O.P. Tree. When the sun rose over the field, what looked like a tree was a tree no longer; rather, it was an exquisitely crafted hunting blind, maximizing personal concealment and observational capacity simultaneously.

You can see photographs, read about the construction of replicant bark, and even learn that some of the trees were internally upholstered — like wartime superfurniture — as snipers sometimes relied on cushions to assist with long periods of sitting, over at the Australian War Memorial.

But there's something almost comedically paranoid about the idea that, upon waking up tomorrow morning, a tree — or rock or, for that matter, a whole hillside — has been surreptitiously replaced by an artificial surrogate, an exactly designed stand-in or double, in a ruse about which you otherwise remain unaware.

It happens again — and again, perhaps for an entire season — before one day you finally stumble upon incontrovertible evidence that the entire forest through which you hike every weekend has been filled with incredibly precise, hollow representations of trees through which someone appears to be spying on you.